Vehicle control system and method

ABSTRACT

Embodiments of the present invention provide a control system for a motor vehicle, the system being operable in a manual operating mode selection condition in which a user may select a required system operating mode by means of user-operable mode selection input means, and an automatic mode selection condition in which the system is configured to select automatically an appropriate system operating mode, wherein when operating in the manual condition and a change from the manual condition to the automatic condition is made the system is configured to select a prescribed automatic mode selection condition vehicle ride-height independently of the selected operating mode.

INCORPORATION BY REFERENCE

The entire contents of co-pending UK patent application numbersGB1111288.5, GB1211910.3 and GB1202427.9 and UK patents GB2325716,GB2308415, GB2341430, GB2382158 and GB2381597 are expressly incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a vehicle control system for one ormore vehicle subsystems and to a method of controlling one or morevehicle subsystems.

BACKGROUND

It is known to provide a vehicle having a plurality of subsystems whichcan be operated in different configurations to suit different drivingconditions. For example, automatic transmissions may be controlled in avariety of modes such as sport, manual, winter or economy. In each mode,subsystem control parameters such as accelerator pedal response andconditions under which changes between gear ratios take place may bemodified so as to suit the conditions of the terrain or the particulartaste of the driver. It is also known to provide air suspensions withon-road and off-road modes. Stability control systems can be operated atreduced activity in certain modes so as to give the driver more directcontrol, and power steering systems can be operated in different modesto provide a varying level of assistance depending on drivingconditions.

It is also known to provide air suspensions with on-road and off-roadmodes. Stability control systems can be operated at reduced activity incertain modes so as to give the driver more direct control, and powersteering systems can be operated in different modes to provide a varyinglevel of assistance depending on driving conditions.

It is desirable to provide an improved control system for a motorvehicle operable in different configurations.

STATEMENT OF THE INVENTION

Embodiments of the invention may be understood with reference to theappended claims.

Aspects of the present invention provide a control system, a vehicle anda method. Control systems according to embodiments of the presentinvention are suitable for a range of different vehicles includingconventional engine-only vehicles, electric vehicles, and/or hybridelectric vehicles.

In one aspect of the invention for which protection is sought there isprovided a control system for a motor vehicle, the system being operablein a manual operating mode selection condition in which a user mayselect a required system operating mode by means of user-operable modeselection input means, and an automatic mode selection condition inwhich the system selects automatically an appropriate system operatingmode, wherein when operating in the manual condition and a change fromthe manual condition to the automatic condition is made the systemselects a prescribed automatic mode selection condition vehicleride-height independently of the automatically selected operating mode.

Embodiments of the invention have the advantage that if whilst operatingin the automatic selection condition changes in operating mode takeplace, a ride height of the vehicle is not changed. This may reduce thenumber of times a change in ride height is effected whilst operating inthe automatic mode selection condition.

Optionally, the operating modes are control modes of at least onesubsystem of a vehicle, the system comprising a subsystem controller forinitiating control of the or each of the vehicle subsystems in theselected one of the plurality of subsystem control modes, each one ofthe operating modes corresponding to one or more different drivingconditions for the vehicle.

The system may comprise evaluation means for evaluating one or moredriving condition indicators to determine the extent to which each ofthe subsystem control modes is appropriate.

Optionally, when in the automatic condition the system is configuredautomatically to control the subsystem controller to initiate control ofthe or each subsystem in the subsystem control mode which is mostappropriate.

Thus, the system operating modes may each correspond to one of aplurality of different driving conditions.

Optionally, the operating modes are control modes of at least onevehicle subsystem selected from amongst an engine management system, atransmission system, a steering system, a brakes system and a suspensionsystem.

Optionally, the operating modes are control modes of at least twovehicle subsystems selected from amongst an engine management system, atransmission system, a steering system, a brakes system and a suspensionsystem.

The operating modes may be control modes of each of those systems.

Optionally, in each system operating mode the system is configured tocause each one of a plurality of vehicle subsystems to be operated in asubsystem configuration mode appropriate to the driving condition.

For example, in the case of a vehicle sub-system in the form of asuspension system operable at a plurality of different ride-heights fora given vehicle loading, the subsystem configuration modes may includemodes corresponding to different respective ride heights. In the case ofa vehicle sub-system controller in the form of an engine or powertraincontroller, the controller may be operable to provide differentrespective values of engine torque as a function of accelerator pedalposition in each of a plurality of different powertrain controllerconfiguration modes. A subsystem control mode may therefore correspondto a set of subsystem configuration modes, for example one configurationmode for each subsystem. For example in one operating mode a ‘high’ rideheight subsystem configuration mode may be set for the suspension systemand a ‘slow’ accelerator pedal map subsystem configuration mode may beset for the powertrain controller. Some subsystems may allow twodifferent parameters to be set. Thus the suspension system may allow aroll stiffness setting of the suspension to be set to one of a pluralityof configuration modes such as low, medium or high.

Various possible known subsystem configuration modes will new bedescribed. The reader is referred to US2003/0200016 for further detailsin respect of known types of subsystem configuration mode and the mannerin which the configuration modes may be implemented. Other configurationmodes are also useful. Other subsystems may also be controlled, inaddition or instead.

Optionally, the operating modes include control modes of a suspensionsystem and the plurality of subsystem configuration modes comprise aplurality of ride heights.

It is to be understood that when the system is operating in theautomatic mode selection configuration, the system is configured toselect a prescribed configuration mode of the suspension system whichcorresponds to the automatic mode selection condition vehicleride-height from amongst a plurality of ride heights that the suspensionsystem is otherwise capable of providing. The prescribed configurationmode may provide the prescribed automatic mode selection conditionvehicle ride-height, being a ride height that is considered to provideadequate clearance for obstacles in any operating mode that the systemmay be permitted to select when operating in the automatic operatingmode selection condition.

Optionally, the subsystem configuration modes of the suspension systeminclude a first ride height and a second ride height greater than thefirst, the system being configured when in the automatic mode selectioncondition automatically to cause a suspension system to assume thesubsystem configuration mode corresponding to the second ride height.

The second ride height therefore corresponds to the automatic modeselection condition vehicle ride-height.

The suspension system may be a fluid suspension system. The fluidemployed by the suspension system may by a gas such as air. The fieldmay be a liquid in some alternative embodiments.

Optionally, the subsystem configuration modes of the suspension systeminclude modes having N+N′ different respective ride heights, where N andN′ are integer, N≧1 and N′≧1, the system being configured to choose asuspension subsystem configuration mode having one of the N highest rideheights when the system is in the automatic operating mode selectioncondition.

Thus the prescribed automatic mode selection condition vehicleride-height may be permitted to take one of N values. The selected oneof the N values may be determined in dependence on one or moreparameters. The one or more parameters may include the identity of theoperating mode that the system selects whilst operating in the automaticoperating mode selection condition.

Thus the system may for example be permitted to choose a suspensionsubsystem configuration mode providing one of 2 ride heights fromamongst 3 or more available ride heights, or any one of 3 ride heightsfrom 4 or more available ride heights. The ride heights the system ispermitted to choose may be ride heights that are deemed, between them,to provide adequate clearance for obstacles in any operating mode thatthe system may be permitted to select when operating in the automaticmode selection condition.

In some embodiments the system may choose one amongst a ‘low’ rideheight a ‘standard’ ride height that is higher than the low ride height,a ‘high’ ride height that is higher than the standard ride height, and a‘maximum’ ride height that is higher than the high ride height. Thesystem may be configured to select the ‘high’ ride height when operatingin the automatic operating mode selection condition, unless a prescribedone or more operating modes are automatically selected. If theprescribed one or more operating modes are automatically selected, thesuspension system may be caused to assume a suspension subsystemconfiguration mode that causes the maximum ride height to be assumed. Insome embodiments, the maximum ride height configuration mode may beassumed for example if it is determined that a vehicle is wading in someembodiments. In some embodiments the maximum ride height may be assumedif the system selects automatically the rock crawl operating mode. Otherarrangements are useful if is to be understood that in some embodimentsthe maximum ride height may be assumed only in relatively unusualcircumstances, such as when wading. The more limited choice of rideheights when operating in the automatic mode selection condition may beadvantageous in reducing the number of changes in ride height during thecourse of a journey in the automatic operating mode selection condition.

Optionally, the operating modes include control modes of a fluidsuspension system in which fluid interconnection can be made betweensuspensions for wheels on opposite sides of the vehicle, and whereinsaid plurality of subsystem configuration modes provide different levelsof said interconnection.

Optionally, the operating modes include control modes of a steeringsystem which can provide steering assistance, and wherein said pluralityof subsystem configuration modes provide different levels of saidsteering assistance.

Optionally, the operating modes include control modes of a brakes systemwhich can provide braking assistance, and said plurality of subsystemconfiguration modes provide different levels of said braking assistance.

Optionally, the operating modes include control modes of a brake controlsystem which can provide an anti-lock function to control wheel slip,and said plurality of subsystem configuration modes allow differentlevels of said wheel slip.

Optionally, the operating modes include control modes of a tractioncontrol system which is arranged to control wheel spin, and saidplurality of subsystem configuration modes allow different levels ofsaid wheel spin.

Optionally, the operating modes include control modes of a yaw controlsystem which is arranged to control vehicle yaw, and said plurality ofsubsystem configuration modes allow different levels of divergence ofsaid vehicle yaw from an expected yaw.

Optionally, the operating modes include control modes of a range changetransmission and said subsystem configuration modes may include a highrange mode and a low range mode of said transmission.

The range change transmission may for example by comprised by a powertransfer unit or power take-off unit for coupling a prop shaft of adriveline to a torque transmission path from an engine or transmissionof the vehicle, such as an automatic transmission.

Optionally, the operating modes include control modes of a powertrainsystem which includes a powertrain control means and an accelerator orthrottle pedal, the subsystem configuration modes providing differentlevels of responsiveness of the powertrain control means to movement ofthe accelerator or throttle pedal.

Optionally, the operating modes include control modes of a transmissionsystem operable in a plurality of transmission ratios and including atransmission control means such as an electronic transmission controllerarranged to monitor at least one parameter of the vehicle and to selectfile transmission ratios in response, and wherein the subsystemconfiguration modes include a plurality of transmission configurationmodes in which the transmission ratios are selected differently inresponse to said at least one parameter.

One of the subsystems may comprise a differential system configured toprovide a plurality of levels of differential lock, and the subsystemconfiguration modes may be arranged to provide different levels of saidlock.

The differential system may be arranged to control the level ofdifferential lock on the basis of a plurality of inputs, audio responddifferently to said inputs in each of the modes.

The differential system may comprise a centre differential, a frontdifferential and/or a rear differential. The differential may be aclutch-based system in some embodiments, whereby differences in rates ofrotation of wheels is accommodated by slipping of a clutch rather thanby means of a conventional differential gear arrangement in which sidewheels are coupled via pinion wheels supported by a differential cage inorder to allow relative rotation.

One of the subsystems may comprise a vehicle body roll control systemarranged to provide body roll correction to reduce vehicle body roll andthe subsystem configuration modes provide different levels of body rollcorrection of the vehicle, at least under some driving conditions.

One of the subsystems may comprise a speed control system arranged tocontrol the speed of the vehicle when descending a hill. The speedcontrol system may be arranged to control the vehicle to differentspeeds in the different configuration modes.

Optionally, the operating modes may include an off-road mode in whichthe subsystems are controlled in a manner suitable for driving on roughterrain and an on-read mode in which the subsystems are controlled in amanner suitable for driving on-road.

Optionally the suspension system is arranged to provide a higher rideheight in the off read mode than in the on-road mode.

Further optionally, in the off-road mode a higher level of saidinterconnection is provided than in the on-road mode.

The traction control system may be arranged to allow more wheel spin inthe off-road mode than in the on-road mode. Alternatively, in someembodiments the traction control system may be arranged to allow lesswheel spin in the off-road mode than in the on-road mode. The amount ofpermitted slip permitted in an off-road mode may depend on the selectedmode.

Optionally the yaw control system is arranged to allow a higher degreeof said divergence in the off-road mode than in the on-road mode.Alternatively, the yaw control system may be arranged to allow a lowerdegree of said divergence in the off-road mode than in the on-road mode.

Optionally, in the off-road mode the range change transmission isoperated in the low range.

Optionally, in the off-road mode the powertrain control means isarranged to provide lower levels of drive torque, for a givenaccelerator or throttle pedal position, at least at low levels ofaccelerator pedal depression, than in the on-road mode.

Optionally, the differential system is arranged to provide higher levelsof differential lock in the off-road mode than in the on-road mode.

Optionally, the roll control system is arranged to provide a higher rollstiffness in the on-road mode than in the off-road mode.

Optionally, the speed control system is arranged to be switched on inthe off-road mode and switched off in the on-road mode.

Optionally, the driving modes include at least one low friction mode inwhich the subsystems are controlled in a manner suitable for driving onlow friction surfaces and a high friction mode in which the subsystemsare controlled in a manner suitable for driving on high frictionsurfaces.

Optionally, the brake control system allows higher levels of slip in thehigh friction mode than in the low friction mode.

Optionally, the traction control system allows higher levels of wheelspin in the high friction mode than in the low friction mode.

Optionally, the braking control system provides a greater level ofbraking assistance in the high friction mode than in the low frictionmode.

Optionally, the powertrain control means is arranged to provide lowerlevels of drive torque, for a given accelerator or throttle pedalposition, at least at low levels of accelerator pedal depression, in thelow friction mode than in the high friction mode.

Optionally, the transmission system is arranged to operate in highergears for a given value of said at least one parameter in the highfriction mode than in the low friction mode.

Optionally, the differential system is arranged to provide higher levelsof differential lock in the low friction mode than in the high frictionmode.

Optionally, the high friction mode may comprise a standard or defaultmode in which the vehicle will operate normally and which is suitablefor on-road driving.

Optionally, there are at least two such low friction modes and thesuspension system is arranged to provide a higher ride height in one ofthe low friction modes than in the other.

Further optionally, there are at least two such low friction modes andthe suspension system is arranged to provide a higher level of saidcross linking in one of the low friction modes than in the other.

Optionally, the at least two low friction modes may comprise a mud modesuitable for traveling through deep mud, and another low friction modesuitable for driving in snow, on grass, or on gravel.

Optionally there may be a plurality of low friction modes, one of whichmay be a grass mode in which the subsystems are controlled in a mannersuitable for driving on grass, one of which may be an ice mode in whichthe subsystems are controlled in a manner suitable for driving in ice,and one of which may be a mud mode in which the subsystems arecontrolled in a manner suitable for driving on mud.

Optionally one of the modes is a sand mode in which the subsystems arecontrolled in a manner suitable for driving on sand. At least one of thesubsystems may be arranged, in the sand mode, to allow only relativelylow levels of wheel spin when the vehicle is traveling at low speeds soas to avoid the vehicle wheals becoming submerged in sand, but to allowrelatively high levels of wheel spin when the vehicle is traveling athigher speeds. Optionally, in the sand mode, the powertrain controlsystem is arranged to provide relatively low levels of drive torque fora given throttle pedal position at low vehicle speeds and to providerelatively high levels of drive torque for a given throttle pedalposition at higher vehicle speeds.

The off-road mode may be a rock crawl mode in which the subsystems arecontrolled in a manner suitable for driving over rocks. Alternatively itmay be set up for more general off-road use. One or more other off-roadmodes may be provided in addition or instead.

One of the modes may be a rough-road mode in which the subsystems arecontrolled in a manner suitable for driving on rough roads, for examplefor driving at relatively high speeds over rough surfaces.

At least one of the modes may be a plough surface mode in which thebrake control subsystem is arranged to allow a relatively high degree ofwheel slip under braking. This may be useful, for example on snow orsand, where the build-up of matter in front of the wheels under brakingcan improve braking performance.

Optionally, at least one of the modes is an on-road mode in which thesubsystems are controlled in a manner suitable for driving on-road. Forexample, one of the modes may be a motorway mode in which the subsystemsare controlled in a manner suitable for driving at high speed on a flatmad surface. One of the modes may be a country road mode in which thesubsystems are controlled in a manner suitable for driving on countryroads.

The driving modes may be selectable by means of at least two inputs, oneof which may be a terrain selection input arranged to influence the modeselected on the basis of the terrain selected, and the other of whichmay be a mode of use input arranged to influence the mode selected onthe basis of a selected mode of use of the vehicle. Each of these inputsmay be user-controlled inputs, or may be derived from one or moresensors.

The mode of use input may be arranged to allow selection between aplurality of driving styles, which may include, for example, a normalstyle, a sport style, and an economy style. Alternatively, or inaddition, the mode of use input may be arranged to allow selectionbetween a plurality of states of the vehicle, for example including atowing state or a loaded state.

The system may be configured to cause a change in ride-height independence on a speed of the vehicle.

The system may be configured when in the automatic mode selectioncondition to reduce ride height below the automatic mode selectioncondition vehicle ride-height when a speed of the vehicle exceeds aprescribed value.

The system may be configured to select a first speed ride height whenthe vehicle speed is above a first prescribed value and a second speedride height greater than the first when the vehicle speed is below asecond prescribed value. The first and second prescribed values of speedmay be the same. Alternatively the first speed value may be higher thanthe second in order to introduce a hysteresis in respect of ride heightas a function of speed and thereby reduce mode chattering. It is to beunderstood that in some embodiments, lowering of ride-height from araised value has the advantage that vehicle stability may be enhanced athigher speeds. An advantageous decrease in aerodynamic drag may also beenjoyed.

As noted above, in some embodiments the vehicle may be configured toassume two or more different ride-heights. In some embodiments thevehicle may be configured to assume a first ride-height, a secondride-height, a third ride-height or a fourth ride-height. The firstride-height may be a ‘default’ or ‘nominal’ ‘on-road’ ride-heightselected when driving on-road. The second ride-height may be higher thanthe first and suitable for driving in off-road conditions such as overmud and ruts. It may be referred to as a ‘raised ride height’. The thirdride-height may be lower than the first and correspond to a ‘kneeling’or ‘access’ ride-height. This ride-height may be selected in order toallow more convenient loading of the vehicle with cargo or passengers.

The fourth ride-height may have a value between the first and thirdride-height values and may be assumed automatically when driving above aprescribed speed on-road, allowing a reduction in vehicle windresistance. This ride-height may be referred to as a ‘highway cruise’ride-height. The prescribed speed may have a value of around 0.50 milesper hour although other arrangements are also useful.

Optionally, if the system determines that the vehicle is towing a load,automatic assumption of the prescribed automatic mode selectioncondition vehicle ride-height is suspended.

Thus, if the system assumes the automatic mode selection condition andthe system determines that the vehicle is towing a load, the system maybe configured not to assume the automatic mode selection conditionvehicle ride-height if the automatic mode selection condition vehicleride-height has not already been assumed. If the automatic modeselection condition vehicle ride-height has already been assumed and thesystem determines that the vehicle is towing a load, the system may beconfigured not to permit a change in ride-height unless a driverover-rides and forces a change in ride-height.

This has the advantage that if the prescribed automatic mode selectioncondition vehicle ride-height is different from the presently selectedride-height, the ride-height will not be changed. It is to be understoodthat changing the ride-height (for example by raising the ride-height)may be undesirable if a trailer is connected to the vehicle sincechanging the ride-height may have an adverse effect on trailerstability, particularly if the trailer has multiple axles.

In some embodiments, the system may be configured automatically to raiseride height from the default or nominal value (or kneeling ride-height)if the user manually selects (with the system in the manual condition)the low range of operation of a range change transmission such as apower take-off unit in a prescribed one or more operating modes (andoptionally for all operating modes). The raising of the ride height maybe delayed or otherwise postponed unless and until the vehicle movesaway from rest and/or until the system determines all vehicle doors areclosed.

In some embodiments the system may suspend allowance of raising of theride-height in response to user manual request via a control input untila warning has been provided to the user, optionally via a display suchas an HMI display. The system may demand that a driver acknowledge thewarning before the system allows the change in ride-height. For examplethe driver may acknowledge the warning by momentarily releasing aride-height adjuster control such as a button and then repeating thedesired manual selection. This feature has the advantage that a user maybe reminded of potential consequences of ride-height adjustment; if thevehicle is towing, trailer stability may be compromised by a ride-heightadjustment, for example.

As noted above, advantageously the system may be configured to maintainthe prescribed automatic mode selection condition vehicle ride-heightwhen operating in the automatic selection condition unless the vehiclespeed exceeds a prescribed value.

In some embodiments, certain vehicle operating modes may only beavailable in a prescribed one or more ranges of a range changetransmission such as a power transfer unit (or power take-off unit). Inthis case, if a user selects the automatic operating mode selectioncondition the system may request a user or driver to set an appropriaterange. The system may then select automatically the most appropriateoperating mode than is allowed in the presently selected range. Thesystem may then suspend changes in ride-height when the system changesautomatically the selected operating mode, so as to avoid repeatedraising and lowering of the ride height.

In some embodiments, if the user selects automatic operating modeselection condition and a low range of the range change transmission,the system may cause a suspension system to assume a raised ride-heightconfiguration mode. The suspension system may be caused to remain in theraised ride-height configuration mode whilst in the automatic operatingmode selection condition.

Optionally, one or more of the driving conditions correspond to one ormore driving surfaces.

In a further aspect of the invention for which protection is soughtthere is provided a method of controlling a motor vehicle implemented bya control system, the method comprising causing the system to operate ina manual operating mode selection condition in which a user may select arequired system operating mode by means of user-operable mode selectioninput means, or in an automatic mode selection condition in which thesystem is configured to select automatically an appropriate systemoperating mode,

-   -   whereby when the system is operating in the manual condition and        a change from the manual condition to the automatic condition is        made the method comprises selecting a prescribed automatic mode        selection condition vehicle ride-height independently of the        selected operating mode.

Optionally, the method comprises causing the vehicle to assume theprescribed automatic mode selection condition vehicle ride-heightindependently of the selected operating mode when the system operates inthe automatic operating mode selection condition.

In a further aspect of the invention for which protection is soughtthere is provided a carrier medium carrying computer readable code forcontrolling a vehicle to carry out a method according to an aspect ofthe invention.

In an aspect of the invention for which protection is sought there isprovided a motor vehicle control system for selecting a driving surfaceand for controlling a plurality of vehicle subsystems to operate in aplurality of subsystem configuration modes in dependence on the selecteddriving surface, the system being operable in a manual operatingcondition in which a user is able to select said driving surface and anautomatic operating condition in which the system is configured toselect said driving surface automatically, wherein the system is able tobe switched between said manual and automatic operating conditions bymeans of a user-operable input device,

-   -   the system being further configured to select a prescribed        vehicle ride-height independently of the selected operating mode        when operating in the automatic selection condition.

It is to be understood that when operating in the manual selectioncondition, the control system may be configured to allow a certain oneor more operating modes to be selected only if a prescribed ride-heighthas already been selected. In some embodiments the user may be requiredto raise or lower the ride-height manually, by means of a ride-heightcontrol switch, before the control mode may be selected. That is, thesystem is not configured automatically to raise or lower the ride when agiven mode is selected.

It is to be understood that if whilst operating in the automatic modeselection condition the system changed ride-height automatically suchthat in a certain one or more prescribed modes one ride-height wasselected and in a certain one or more other prescribed modes anotherride-height was selected, the ride-height might vary repeatedly over thecourse of a given journey if multiple mode changes take place.Accordingly, embodiments of the invention have the advantage that thenumber of changes in ride-height that may be made whilst operating inautomatic mode may be reduced. This reduces wear of componentsassociated with ride-height changes such as one or more air compressorsin the case of air suspension systems.

Within the scope of this application it is expressly envisaged that thevarious aspects, embodiments, examples and alternatives set cot in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

For the avoidance of doubt, it is to be understood that featuresdescribed with respect to one aspect of the invention may be includedwithin any other aspect of the invention, alone or in appropriatecombination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by wayof example only, with reference to the accompanying figure in which:

FIG. 1 is a schematic illustration of a vehicle according to anembodiment of the present invention;

FIG. 2 is a block diagram to illustrate a vehicle control system inaccordance with an embodiment of the invention, including variousvehicle subsystems under the control of the vehicle control system;

FIG. 3 is a table showing which vehicle subsystem configuration mode isselected in each respective vehicle operating mode;

FIG. 4 is a schematic illustration of a switchpack according to anembodiment of the invention with a rotary knob in a deployed condition;

FIG. 5 is a schematic illustration of a switchpack according to anembodiment of the invention with a rotary knob in a retracted condition;and

FIG. 6 is a flow diagram illustrating a method of operation of a vehicleaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle 100 according to an embodiment of the inventionintended to be suitable for off-road use, that is for use on terrainsother than regular tarmac road, as well as on-road. The vehicle 100 hasa powertrain 129 that includes an engine 121 that is connected to adriveline 130 having a transmission 124. In the embodiment shown thetransmission 124 is an automatic transmission 124. Embodiments of thepresent invention are also suitable for use in vehicles with a manualtransmission, continuously variable transmission or any other suitabletransmission.

The driveline 130 is arranged to drive a pair of front vehicle wheels111,112 by means of a front differential 135F and a pair affront driveshafts 118. The driveline 130 also comprises an auxiliary drivelineportion 131 arranged to drive a pair of rear wheels 114, 115 by means ofan auxiliary driveshaft or prop-shaft 132, a rear differential 135 and apair of rear driveshafts 139. Embodiments of the invention are suitablefor use with vehicles in which the transmission is arranged to driveonly a pair of front wheels or only a pair of rear wheels (i.e. frontwheel drive vehicles or rear wheel drive vehicles) or selectable twowheel drive/four wheel drive vehicles. In the embodiment of FIG. 1 thetransmission 124 is releasably connectable to the auxiliary drivelineportion 131 by means of a power transfer unit (PTU) 137, allowingselectable two wheel drive or four wheel drive operation. It is to beunderstood that embodiments of the invention may be suitable forvehicles having more than four wheels or where only two wheels aredriven, for example two wheels of a three wheeled vehicle or fourwheeled vehicle or a vehicle with more than four wheels.

The PTU 137 is operable in a ‘high ratio’ or a ‘low ratio’configuration, in which a gear ratio between an input shaft and anoutput shaft thereof is selected to be a high or low ratio. The highratio configuration is suitable for general on-road or ‘on-highway’operations whilst the low ratio configuration is more suitable fornegotiating certain off-road terrain conditions and other low speedapplications such as towing.

The vehicle 100 has an accelerator pedal 161, brake pedal 163 andsteering wheel 181. The steering wheel 181 has a cruise control selectorbutton 181C mounted thereto for activating a cruise control system 11.

The vehicle 100 has a central controller, referred to as a vehiclecontrol unit (VCU) 10. The VCU 10 receives and outputs a plurality ofsignals to and from various sensors and subsystems 12 provided on thevehicle 100.

FIG. 2 shows the VCU 10 in more detail. The VCU 10 controls a pluralityof vehicle subsystems 12 including, but not limited to, an enginemanagement system 12 a, a transmission system 12 b, an electronic powerassisted steering unit 12 c (ePAS unit), a brakes system 12 d and asuspension system 12 e. Although five subsystems are illustrated asbeing under the control of the VCU 10, in practice a greater number ofvehicle subsystems may be included on the vehicle and may be under thecontrol of the VCU 10. The VCU 10 includes a subsystem control module 14which provides control signals via line 13 to each of the vehiclesubsystems 12 to initiate control of the subsystems in a mannerappropriate to the driving condition, such as the terrain, in which thevehicle is travelling (referred to as the terrain condition). Thesubsystems 12 also communicate with the subsystems control module 14 viasignal line 13 to feedback information on subsystem status. In someembodiments, instead of an ePAS unit 12 c, a hydraulically operatedpower steering unit may be provided.

The VCU 10 receives a plurality of signals, represented generally at 16and 17, which are received from a plurality of vehicle sensors and arerepresentative of a variety of different parameters associated withvehicle motion and status. As described in further detail below, thesignals 16, 17 provide, or are used to calculate, a plurality of drivingcondition indicators (also referred to as terrain indicators) which areindicative of the nature of the condition in which the vehicle istravelling. One advantageous feature of some embodiments of the presentinvention is that the VCU 10 determines the most appropriate controlmode for the various subsystems on the basis of the terrain indicators,and automatically controls the subsystems accordingly. That is, the VCU10 determines the most appropriate control mode on the basis of theterrain indicators and automatically causes each of the subsystems 12 tooperate in the respective subsystem configuration mode corresponding tothat control mode.

The sensors (not shown) on the vehicle include, but are not limited to,sensors which provide continuous sensor outputs 16 to the VCU 10,including wheel speed sensors, an ambient temperature sensor, anatmospheric pressure sensor, tyre pressure sensors, yaw sensors todefect yaw, roll and pitch of the vehicle, a vehicle speed sensor, alongitudinal acceleration sensor, an engine torque sensor (or enginetorque estimator), a steering angle sensor, a steering wheel speedsensor, a gradient sensor (or gradient estimator), a lateralacceleration sensor (part of a stability control system (SCS)), a brakepedal position sensor, an acceleration pedal position sensor andlongitudinal, lateral, vertical motion sensors.

In other embodiments, only a selection of the aforementioned sensors maybe used. The VCU 10 also receives a signal from the electronic powerassisted steering unit (ePAS unit 12 c) of the vehicle to indicate thesteering force that is applied to the wheels (steering force applied bythe driver combined with steering force applied by the ePAS unit 12 c).

The vehicle 100 is also provided with a plurality of sensors whichprovide discrete sensor output signals 17 to the VCU 10, including acruise control status signal (ON/OFF), a transfer box or PTU 137 statussignal (whether the gear ratio is set to a HI range or a LO range), aHill Descent Control (HDC) status signal (ON/OFF), a trailer connectstatus signal (ON/OFF), a signal to indicate that the Stability ControlSystem (SCS) has been activated (ON/OFF), a windscreen wiper signal(ON/OFF), an air suspension ride-height status signal (HI/LO), and aDynamic Stability Control (DSC) signal (ON/OFF).

The VCU 10 includes an evaluation means in the form of an estimatormodule or processor 18 and a calculation and selection means in the formof a selector module or processor 20. Initially the continuous outputs16 from the sensors are provided to the estimator module 18 whereas thediscrete signals 17 are provided to the selector module 20.

Within a first stage of the estimator module 18, various ones of thesensor outputs 16 are used to derive a number of terrain indicators. Ina first stage of the estimator module 18, a vehicle speed is derivedfrom the wheel speed sensors, wheel acceleration is derived from thewheel speed sensors, the longitudinal force on the wheels is derivedfrom the vehicle longitudinal acceleration sensor, and the torque atwhich wheel slip occurs (if wheel slip occurs) is derived from themotion sensors arranged to detect yaw, pitch and roll. Othercalculations performed within the first stage of the estimator module 18include the wheel inertia torque (the torque associated withaccelerating or decelerating the rotating wheels), “continuity ofprogress” (the assessment of whether the vehicle is starting andstopping, for example as may be the case when the vehicle is travellingover rocky terrain), aerodynamic drag, yaw rate, and lateral vehicleacceleration.

The estimator module 18 also includes a second stage in which thefollowing terrain indicators are calculated: surface rolling resistance(based on the wheel inertia torque, the longitudinal force on thevehicle, aerodynamic drag, and the longitudinal force on the wheels),the steering force on the steering wheel 181 (based on the lateralacceleration and the output from the steering wheel sensor), the wheellongitudinal slip (based on the longitudinal force on the wheels, thewheel acceleration, SCS activity and a signal indicative of whetherwheel clip has occurred), lateral friction (calculated from the measuredlateral acceleration and the yaw versus the predicted lateralacceleration and yaw), and corrugation detection (high frequency, lowamplitude wheel height excitement indicative of a washboard typesurface).

The SCS activity signal is derived from several outputs from an SCS ECU(not shown), which contains the DSC (Dynamic Stability Control)function, the TC (Traction Control) function, ABS and HDC algorithms,indicating DSC activity, TC activity, ABS activity, brake interventionson individual wheels, and engine torque reduction requests from the SCSECU to the engine. All these indicate a slip event has occurred and theSCS ECU has taken action to control it. The estimator module 18 alsouses the outputs from the wheel speed sensors to determine a wheel speedvariation and corrugation defection signal.

On the basis of the windscreen wiper signal (ON/OFF), the estimatormodule 18 also calculates how long the windscreen wipers have been in anON state (i.e. a rain duration signal).

The VCU 10 also includes a read roughness module 24 for calculating theterrain roughness based on the air suspension sensors (the ride heightsensors) and the wheel accelerometers. A terrain indicator signal in theform of a roughness output signal 26 is output from the road roughnessmodule 24.

The estimates for the wheel longitudinal slip and the lateral frictionestimation are compared with one another within the estimator module 18as a plausibility check.

Calculations for wheel speed variation and corrugation output, thesurface rolling resistance estimation, the wheel longitudinal slip andthe corrugation defection, together with the friction plausibilitycheck, are output from the estimator module 18 and provide terrainindicator output signals 22, indicative of the nature of the terrain inwhich the vehicle is travelling, for further processing within the VCU10.

The terrain indicator signals 22 from the estimator module 18 areprovided to the selector module 20 for determining which of a pluralityof vehicle subsystem control modes (and therefore correspondingsubsystem configuration modes) is most appropriate based on theindicators of the type of terrain in which the vehicle is travelling.The most appropriate control mode is determined by analysing theprobability that each of the different control modes is appropriate onthe basis of the terrain indicator signals 22, 26 from the estimatormodule 18 and the road roughness module 24.

The vehicle subsystems 12 may be controlled automatically in a givensubsystem control mode (in an “automatic mode” or “automatic condition”of operation of the VCU 10) in response to a control output signal 30from the selector module 20 and without the need for driver input.Alternatively, the vehicle subsystems 12 may be operated in a givensubsystem control mode according to a manual user input (in a “manualmode” or “manual condition” of operation of the VCU 10) via a HumanMachine Interface (HMI) module 32. Thus the user determines in whichsubsystem control mode the subsystems will be operated by selection of arequired system control mode (operating mode). The HMI module 32comprises a display screen (not shown) and a user operable switchpack170 (FIG. 4). The user may select between the manual and automatic modes(or conditions) of operation of the VCU 10 via the switchpack 170. Whenthe VCU 10 is operating in the manual mode or condition, the switchpack170 also allows the user to select the desired subsystem control mode.

It is to be understood that the subsystem: controller 14 may itselfcontrol the vehicle subsystems 12 a-12 e directly via the signal line13, or alternatively each subsystem may be provided with its ownassociated intermediate controller (not shown in FIG. 1) for providingcontrol of the relevant subsystem 12 a-12 e. In the latter case thesubsystem controller 14 may only control the selection of the mostappropriate subsystem control mode for the subsystems 12 a-12 e, ratherthan implementing the actual control steps for the subsystems. The oreach intermediate controller may in practice form an integral part ofthe main subsystem controller 14.

When operating in the automatic mode, the selection of the mostappropriate subsystem control mode may be achieved by means of a threephase process:

(1) for each type of control mode, a calculation is performed of theprobability that the control mode is suitable for the terrain over whichthe vehicle is travelling, based on the terrain indicators;

(2) the integration of “positive differences” between the probabilityfor the current control mode and the other control modes; and

(3) the program request to the control module 14 when the integrationvalue exceeds a pre-determined threshold or the current terrain controlmode probability is zero.

The specific steps for phases (1), (2) and (3) will now be described inmore detail.

In phase (1), the continuous terrain indicator signals in the form ofthe road surface roughness output 26 and the outputs 22 from theestimator module 18 are provided to the selector module 20. The selectormodule 20 also receives the discrete terrain indicators 17 directly fromvarious sensors on the vehicle, including the transfer box status signal(whether the gear ratio is set to a HI range or a LO range), the DSCstatus signal, cruise control status (whether the vehicle's cruisecontrol system 11 is ON or OFF), and trailer connect status (whether ornot a trailer is connected to the vehicle). Terrain indicator signalsindicative of ambient temperature and atmospheric pressure are alsoprovided to the selector module 20.

The selector module 20 is provided with a probability algorithm 20 a forcalculating the most suitable control mode for the vehicle subsystemsbased on the discrete terrain indicator signals 17 received directlyfrom the sensors and the continuous terrain indicators 22, 26 calculatedby the estimator module 18 and the road surface roughness module 24,respectively. That is, the probability algorithm 20 a calculates themost suitable system control mode, which determines the respectivesubsystem configuration mode in which each subsystem is to be operated,based on the discrete terrain indicator signals 17.

The control modes typically include a grass/gravel/snow control mode(GGS mode) that is suitable for when the vehicle is travelling in grass,gravel or snow terrain, a mud/ruts control mode (MR mode) which issuitable for when the vehicle is travelling in mud and ruts terrain, arock crawl/boulder mode (RB mode) which is suitable for when the vehicleis travelling in rock or boulder terrain, a sand mode which is suitablefor when the vehicle is travelling in sand terrain (or deep soft snow)and a special programs OFF mode (SP OFF mode or SPO mode) which is asuitable compromise mode, or general mode, for all terrain conditionsand especially vehicle travel on motorways and regular roadways. Manyother control modes are also envisaged including those disclosed inUS2003/0200016, the content of which is hereby incorporated byreference.

The different terrain types are grouped according to the friction of theterrain and the roughness of the terrain. For example, it is appropriateto group grass, gravel and snow together as terrains that provide a lowfriction, smooth surface and it is appropriate to group rock and boulderterrains together as high friction, very high roughness terrains.

FIG. 3 is a table taken from US2003/0200016 showing the particularsub-system configuration modes assumed by the subsystems 12 of thevehicle 100 in the respective different operating modes in which the VCU10 may operate.

The operating modes are:

(a) A motorway (or highway) mode;

(b) A country road mode;

(c) A city driving (urban) mode;

(d) A towing (on-road) mode;

(e) A dirt track mode;

(f) A snow/ice (on-road) mode;

(g) A GGS mode;

(h) A sand mode;

(i) A rock crawl or boulder crossing mode; and

(j) A mud/ruts mode

With reference to FIG. 3, the configuration of the suspension system 12e is specified in terms of ride height (high, standard or low) andside/side air interconnection. The suspension system 12 e is a fluidsuspension system, in the present embodiment an air suspension system,allowing fluid interconnection between suspensions for wheels onopposite sides of the vehicle in the manner described in US2003/0200016.The plurality of subsystem configuration modes provide different levelsof said interconnection, in the present case no interconnection(interconnection closed) and at least partial interconnection(interconnection open).

The configuration of the ePAS steering unit 12 c may be adjusted toprovide different levels of steering assistance, wherein steering wheel181 is easier to turn the greater the amount of steering assistance. Theamount of assistance may be proportion to vehicle speed in someoperating modes.

The brakes system 12 d may be arranged to provide relatively high brakeforce for a given amount of pressure applied to the brake pedal 163 or arelatively low brake force, depending on the operating mode.

The brakes system 12 d may also be arranged to allow different levels ofwheel when an anti-lock braking system is active, (relatively lowamounts on low friction (“low-mu” surfaces) and relatively large amountson high friction surfaces).

An electronic traction control (ETC) system may be operated in a high muor low mu configuration, the system tolerating greater wheel slip in thelow mu configuration before intervening in vehicle control compared witha high mu configuration.

A dynamic stability control system (DSC) may also be operated in a highmu or low mu configuration.

The engine management system 12 a may be operated in ‘quick’ or ‘slow’accelerator (or throttle) pedal progression configuration modes in whichan increase in engine torque as a function of accelerator pedalprogression is relatively quick or slow, respectively. The rate may bedependent on speed in one or more modes such as Sand mode.

The PTU 137 may be operated in a high range (HI) subsystem configurationmode or low range (LO) subsystem configuration mode as described herein.

The transmission 124 may be operated in a “normal” mode that provides areasonable compromise between fuel economy and driving performance, a“performance” mode which generally keeps the transmission in lower gearsthan in the normal mode, particularly when the driver is requesting ahigh level of driving torque to accelerate the vehicle, and a “manual”mode in which the control of gear changes is given completely to thedriver. There is also a “snow” or “ice” mode which generally keeps thetransmission in higher gears than the normal mode, in particular underacceleration from rest, to avoid loss of fraction due to wheel spin, anda “sand” mode which keeps the transmission in relatively high gears atlow speed to avoid excessive wheel spin. Excessive wheel spin can resultin the wheels digging themselves into the sand at low speeds. However,the sand mode uses relatively low gears at higher speeds where arelatively high degree of wheel slip can be desirable to provide maximumtraction. Lower gearing also helps the engine 121 to remain in anoperating region where the engine speed is high and the power output ishigh, thereby helping to avoid the vehicle 100 becoming “bogged down” bya lack of power.

In some embodiments, a centre differential and a rear differential eachinclude a clutch pack and are controllable to vary the degree of lockingbetween a “fully open” and a “fully locked” state. The actual degree oflocking at any one time may be controlled on the basis of a number oflectors in a known manner, but the control can be adjusted so that thedifferentials are “more open” or “more locked”. Specifically thepre-load on the clutch pack can be varied which in turn controls thelocking torque, i.e. the torque across the differential that will causethe clutch, and hence the differential to slip. A front differentialcould also be controlled in the same or similar way.

For each subsystem control mode, the algorithm 20 a within the selectormodule 20 performs a probability calculation, based on the terrainindicators, to determine a probability that each of the differentcontrol modes is appropriate. The selector module 20 includes a tuneabledata map which relates the continuous terrain indicators 22, 26 (e.g.vehicle speed, road roughness, steering angle) to a probability that aparticular control mode is appropriate. Each probability value typicallytakes a value of between 0 and 1. So, for example, the vehicle speedcalculation may return a probability of 0.7 for the RB mode if thevehicle speed is relatively slow, whereas if the vehicle speed isrelatively high the probability for the RB mode will be much lower (e.g.0.2). This is because it is much less likely that a high vehicle speedis indicative that the vehicle is travelling over a rock or boulderterrain.

In addition, for each subsystem control mode, each of the discreteterrain indicators 17 (e.g. trailer connection status ON/OFF, cruisecontrol status ON/OFF) is also used to calculate an associatedprobability for each of the control modes, GGS, RB, Sand, MR or SP OFF.So, for example, if cruise control is switched on by the driver of thevehicle, the probability that the SP OFF mode is appropriate isrelatively high, whereas the probability that the MR control mode isappropriate will be lower.

For each of the different sub system control modes, a combinedprobability value, Pb, is calculated based on the individualprobabilities for that control mode, as described above, as derived fromeach of the continuous or discrete terrain indicators 17, 22, 26. In thefollowing equation, for each control mode the individual probability asdetermined for each terrain indicator is represented by a, b, c, d . . .n. The combined probability value, Pb, for each control mode is thencalculated as follows:Pb=(a,b,c,d . . . n)/((a,b,c,d . . . n)+(1−a),(1−b),(1−c),(1−d) . . .(1−n))

Any number of individual probabilities may be input to the probabilityalgorithm 20 a and any one probability value input to the probabilityalgorithm may itself be the output of a combinational probabilityfunction.

Once the combined probability value for each control mode has beencalculated, the subsystem control program corresponding to the controlmode with the highest probability is selected within the selector module20 and an output signal 30 providing an indication of this is providedto the subsystem control module 14. The benefit of using a combinedprobability function based on multiple terrain indicators is thatcertain indicators may make a control mode (e.g. GGS or MR) more or lesslikely when combined together, compared with basing the selection onjust a single terrain indicator alone.

A further control signal 31 from the selector module 20 is provided to acontrol module 34.

In phase (2), an integration process is implemented continually withinthe selector module 20 to determine whether it is necessary to changefrom the current control mode to one of the alternative control modes.

The first step of the integration process is to determine whether thereis a positive difference between the combined probability value for eachof the alternative control modes compared with the combined probabilityvalue for the current control mode.

By way of example, assume the current control mode is GGS with acombined probability value of 0.5. If a combined probability value forthe sand control mode is 0.7, a positive difference is calculatedbetween the two probabilities (i.e. a positive difference value of 0.2).The positive difference value is integrated with respect to time. If thedifference remains positive and the integrated value reaches apredetermined change threshold (referred to as the change threshold), orone of a plurality of predetermined change thresholds, the selectormodule 20 determines that the current terrain control mode (for GGS) isto be updated to a new, alternative control mode (in this example, thesand control mode). A control output signal 30 is then output from theselector module 20 to the subsystem control module 14 to initiate thesand control mode for the vehicle subsystems.

In phase (3), the probability difference is monitored and if, at anypoint during the integration process, the probability difference changesfrom a positive value to a negative value, the integration process iscancelled and reset to zero. Similarly, if the integrated value for oneof the other alternative control modes (i.e. other than sand), reachesthe predetermined change threshold before the probability result for thesand control mode, the integration process for the sand control mode iscancelled and reset to zero and the other alternative control mode, witha higher probability difference, is selected.

HDC Interaction

As described above, the vehicle 100 has an HMI module 32 comprising auser operable switchpack 170 shown schematically in FIG. 4. Theswitchpack 170 allows a user to toggle the VCU 10 between the automaticand manual conditions of operation.

The switchpack 170 has a frame 170F supporting switchgear associatedwith the switchpack 170. The switchpack 170 has a rotary knob 172connected to a multistable rotary switch (not shown). The knob 172 maybe moved between an exposed or deployed position as shown in FIG. 3 anda retracted position as shown in FIG. 5. In the exposed position theknob 172 stands proud of a panel 172P which surrounds the knob 172.Icons 172 a-e are marked in the panel at circumferentially spaced apartlocations around the knob 172 over an arc of around 140° in theembodiment shown although other angles and other numbers of modes arealso useful. The icons 172 a-e may be illuminated selectively in orderto indicate the identity of the control mode in which the subsystems 12are being operated.

Other switches 171 a, b are also provided in a remaining portion of thepanel 172P allowing a driver to activate a hill descent control (HDG)function, via switch 171 a, and select a required gear ratio of the PTU137 (‘high’ or ‘low’), via switch 171 b.

Further switches 171 c of the switchpack enable the SCS system of thevehicle to be activated or deactivated, a ride height to be adjusted(buttons 171 c′), an ‘eco’ mode (arranged to enhance fuel economy) to beselected and an automatic speed limiter (ASL) function to be selected.

The rotary knob 172 has a substantially cylindrical column portion 174with its cylinder axis oriented substantially vertically. The knob 172has an upper panel 175 bearing the word ‘AUTO’. When the knob 172 is inthe refracted position an indicator lamp 175L of the panel 175illuminates, indicating that the VCU 10 has assumed the automaticcondition in which the VCU 10 selects automatically an appropriatesubsystem control mode.

When the knob 172 is in the exposed position the indicator lamp 175L isextinguished, indicating that the VCU 10 has assumed the manualcondition. The knob 172 is moved between the exposed and retractedpositions by means of a spring mechanism triggered by pressing on thepanel 175. Other arrangements are also useful such as an electricalactuator. In some embodiments a switch is integrated into the knob 172such that pressing on the panel 175 alone actuates the switch to switchbetween the automatic and manual conditions. In some embodiments theswitch is positioned such that sufficient axial pressure applied tosubstantially any exposed portion of the knob 172 including rim 172Rresults in actuation of the switch. The knob 172 may be configured toexercise a relatively small axial translation when the switch isactuated, providing tactile feedback to the user, followed by arelatively large axial translation as the knob 172 moves between theexposed and retracted positions or vice versa.

The knob 172 is configured such that the rim 172R may be grasped by theuser and rotated about a cylinder axis of the column portion 174. Theswitchpack 170 is arranged such that the VCU 10 may determine in whichdirection the user turns the rim 172R based on a signal output by theswitchpack 170. In an example rim 172R is provided with a knurledperipheral surface arranged to facilitate the user grasping the knob 172with their fingers.

Rotation of the rim 172R is indexed in discrete angular increments ofaround 10-20° by means of a detent mechanism. This allows tactilefeedback to be provided to a user confirming when the knob 172 has beennotated through one of the discrete angular increments. Other angles andether arrangements are also useful. The rim 172R may be rotated by anynumber of turns in either direction without constraint by the switchpack170.

In some embodiments, when the VCU 10 is in the manual condition,rotation of the rim 172R by two increments in a clockwise (oranticlockwise) direction causes the VCU 10 to assume the modecorresponding to the icon 172 a-e that is located adjacent the iconcorresponding to the currently selected mode in a clockwise (oranticlockwise) direction. If no such icon exists then the VCU 10 takesno action and the currently selected mode remains selected. If the userrotates the knob 172R by only a single increment in a given direction,with no farther increment in that direction within a prescribed timeperiod (such as 1 s or any other suitable period), no change in controlmode takes place. This feature reduces a risk that a userunintentionally changes the selected mode. It is to be understood thatany prescribed number of turns by the incremental amount may be requiredin order to enable a mode change to take place. Furthermore, anyprescribed time period may be set within which the prescribed number ofturns by the incremental amount (or in addition, or instead any twoconsecutive incremental amounts) are to take place. In some embodiments,a user is repaired to rotate the rim 172R by only a single incrementalamount in order to signal a requirement to change mode.

In some embodiments, in addition to or instead of rotating the rim 172Rof the knob 172 in order to change control mode when the VCU 10 is inthe manual condition, the knob 172 may be configured such that modechanges may be effected by rotation of column 174. In some embodimentsthe rim 172R may be ratable whilst the column 174 remains stationary,whilst in some alternative embodiments the rim 172R and column 174 maybe arranged to rotate together. They may for example be fixedly coupledor integrally formed in some embodiments.

In some embodiments, the VCU 10 may be configured to allow manualselection of a given control mode following user selection of that modeonly once it has determined that the user has finished rotating the rim172R. The VCU 10 may wait a prescribed period of time after the lastincremental rotation has been detected, for example up to around 2 s,before allowing a mode change to take place. In some embodiments the VCU10 may be arranged to effect a mode change a predetermined time after ithas been determined that the user has released their grip from the knob172.

In some embodiments the VCU 10 may be arranged to verify that one ormore prescribed vehicle settings or parameters are appropriate to themode the user wishes to select before allowing a mode change. Forexample, the VCU 10 may check one or more selected ham amongst selectedPTU gear ratio, selected ride height and/or one more other settings. Ifthe settings are not appropriate to the mode the user wishes to select,the VCU 10 may be configured to remain in the current control mode untilthe settings are determined to be appropriate. In the meantime the VCU10 may cause the icon of the currently selected mode to remainilluminated. The icon corresponding to that of the mode the user wishesthe VCU 10 to assume may be arranged to illuminate intermittently insome embodiments, e.g. by flashing. The user may be informed of the oneor more deficiencies in settings identified by the VCU 10. If they arenot remedied within a prescribed period of time, or in some embodimentsif an attempt to remedy them is not commenced within a prescribedperiod, the VCU 10 may be configured to operate as if the user had notsought to change mode. That is, information in respect of deficienciesis not displayed any longer, and flashing of the icon corresponding tothe proposed mode is terminated.

It is to be understood that when a user activates the automaticcondition of the VCU 10 the VCU 10 controls the vehicle subsystems tooperate in the most appropriate control mode as determined by the VCU10. The rotary knob 172 assumes the retracted position and any rotationof the rim 172R by a user does not cause a change in the selectedcontrol mode. Rather, it is ignored by the VCU 10.

If whilst the VCU 10 is in the automatic condition the manual conditionis activated, the VCU 10 controls the vehicle subsystems automaticallyto assume the SPO mode, being the mode intended to provide the bestcompromise in vehicle subsystem adjustment/set-up for normal road andlight off-road use. The knob 172 also assumes the exposed position. Icon172 a, which corresponds to the SPO mode, is illuminated.

If a user wishes to select a mode other than the SPO mode, he or she maygrasp the rim 172R and rotate the rim 172R in a clockwise direction toselect the appropriate mode. If the rim 172R is rotated by two indexedangular increments and the user waifs for 2 s, the VCU 10 assumes theGGS mode. Icon 172 a is no longer illuminated and icon 172 b becomesilluminated. If the rim 172R is rotated by two further angularincrements, the vehicle will assume MR mode, icon 172 b will no longerbe illuminated and icon 172 c will be illuminated instead, and so forth.As noted above, the number of angular increments may be any suitablenumber such as 1, 3 or any other suitable number. Any other suitableuser wait period may also be employed.

Thus if is to be understood that the angular position of the rim 172Rwhen the automatic condition was last selected is irrelevant to thedetermination of the control mode the VCU 10 will assume when the manualcondition is subsequently selected. Regardless of the control mode thatwas selected when the knob 172 was last retracted, when the knob 172 issubsequently exposed VCU 10 selects the SPO control mode. Because therim 172R is freely rotatable without constraint (due to the absence offeatures constraining rotation such as an end stop to prevent furtherrotation in a given direction) the actual (absolute) angular position ofthe rim 172R is irrelevant. If is to be understood that if this featurewere not employed and the rim 172R were required to be in a prescribedabsolute rotational position in order to select SPO mode, additional(automatic) actuation of the rim 172R by the switchpack 170 would berequired when transitioning from the automatic to manual conditions ofthe VCU 10. For example, if the rim 172R had been set to select RB modeprior to the user selecting the automatic condition of the VCU 10, theswitchpack 170 would be required to rotate the rim 172R from theposition corresponding to the RB mode to that corresponding to the SPOmode when manual mode were subsequently selected. Additional,potentially complicated failsafe countermeasures would be required.

It is to be understood that in some alternative embodiments, when theautomatic condition is deselected and the manual condition is assumed,the VCU 10 may be arranged to remain in the driving mode that wasselected automatically by the VCU 10 when in the automatic conditionuntil the user selects a different driving mode by rotation of the rim172R. Thus, when the manual condition is selected, the icon 172 a-ecorresponding to the currently (automatically) selected driving moderemains illuminated. If the VCU 10 is configured such that none of icons172 a-e are illuminated when the VCU 10 is in the automatic conditionthen the icon corresponding to the currently selected driving mode isilluminated when the manual condition is assumed.

It is to be understood that other arrangements are also useful.

It is to be understood that when the VCU 10 is operating in the manualcondition, the HDC function may be selected by means of switch 171 a.When active, the HDC function limits a rate of progress (i.e. a speed)of the vehicle 100 overground when descending a slope to a prescribedvalue by application of a foundation braking system of the vehicle 100.In the vehicle 100 of FIG. 1 the foundation braking system is providedby a friction braking system. In some embodiments the foundation brakingsystem may be provided by a regenerative braking system in addition orinstead. HDC functionality is described in UK patents GB2325716,GB2308415, GB2341430, GB2382158 and GB2381597.

It is to be understood that if the vehicle is descending a slope, a usermay activate the HDC function by pressing switch 171 a. The VCU 10 thenassumes control of the foundation braking system and limits the speed atwhich the vehicle 100 may descend the slope to a user-prescribed value.If the vehicle speed drops below the user-prescribed value the user mayincrease the speed by pressing the accelerator pedal 161. If the userwishes to decrease speed below the prescribed value temporarily, forexample if the riser wishes to stop the vehicle, the user may press thebrake pedal 163 to activate the foundation braking system in theexpected manner.

The VCU 10 is configured wherein if the VCU 10 is operating in theautomatic mode selection condition and the user selects the HDCfunction, the VCU 10 activates the HDC function but suspends any furtherautomatic changes in selected sub-system control mode. That is, the VCU10 remains in the presently selected control mode when the HDC functionis selected. If the VCU 10 is operating in the automatic condition, theVCU 10 may be operable to automatically initialise HDC in a standbymode, such that its function may be armed and waiting to intervene whererequired. If HDC intervenes whilst the vehicle is travelling with VCU 10operating in the automatic condition, a control mode change will not bemade during the period for which the HDC function is operating andintervening to maintain composed vehicle progress.

In some embodiments the VCU 10 also suspends determination of the mostappropriate control mode for the terrain over which the vehicle 100 istravelling until the HDC function is deselected. This feature may reducea computational burden placed on the VCU 10 whilst the HDC function isactive in some embodiments.

In some alternative embodiments the VCU 10 continues to determine themost appropriate control mode for the terrain over which the vehicle 100is travelling even whilst the HDC function is active. It is to beunderstood that the reliability of certain terrain indicators used indetermining the terrain over which the vehicle 100 is moving may bereduced during HDC intervention. That is, HDC intervention may give riseto an erroneous determination of the type of terrain over which thevehicle is moving and therefore of the most appropriate control mode.Thus the VCU 10 may wait for a prescribed number of wheel rotations totake place, for a prescribed distance to be travelled or for aprescribed time period to elapse once the HDC intervention has ceasedbefore allowing automatic control mode changes to take place.

In some embodiments the VCU 10 may wait for a prescribed time period toelapse or for a prescribed number of wheel rotations to take place orfor a prescribed distance to be travelled over terrain having a gradientbelow a prescribed value before allowing a change in mode to take placeautomatically.

In some embodiments, when the HDC intervention has ceased, the VCU 10 isarranged to remain in the selected control mode and delay automaticchanging of control mode for a prescribed period of time, optionally aprescribed period of from around 5 s to around 2 minutes before allowinga change in control mode to be made automatically whilst the VCU 10 isin the automatic condition. Other values are also useful.

In some embodiments when the HDC function is deactivated the VCU 10 isarranged to remain in the selected control mode for a prescribeddistance of travel, optionally a distance of from around 2 m to around200 m before allowing a change in control mode to be made automaticallywhilst the VCU 10 is in the automatic condition.

This delay (in distance or time) has the advantage that when the VCU 10returns to automated control mode following cessation of HDCintervention, the vehicle response to the user pressing of the brakeand/or accelerator pedals 163, 161 will be in line with that anticipatedand expected by the user, and consistent with that experienced by thedriver prior to HDC intervention.

In some embodiments, when the VCU 10 activates the HDC function anHDC-specific relationship between accelerator pedal position and torquedeveloped by the powertrain is implemented by the VCU 10. Similarly apredetermined relationship between brake pedal pressure and brake torqueapplied by means of the foundation braking system may be established inaddition or instead. These values may be independent of the control modein which the VCU 10 is operating.

In some alternative embodiments, the form of the response of thepowertrain 129 and braking system to accelerator and brake pedal inputsrespectively is dependent on the selected control mode and correspondsto that implemented when the VCU 10 is in that control mode and the HDCfunction is not active. Thus it is to be understood that in suchembodiments, the fact that changes in control mode are suspended whenthe HDC function is active have the advantage that a response of thevehicle to accelerator and brake pedal inputs does not change whilst theHDC function is active, i.e. because the selected control mode is notchanged. This reduces a risk that a driver is inconvenienced by a changein vehicle response to accelerator and/or brake pedal control inputswhen performing a hill descent operation.

Some embodiments of the present invention have the advantage thatvehicle composure may be preserved and in some embodiments or situationscomposure may be enhanced. Some embodiments have the advantage that userconfidence in vehicle operation performance and expected response may beenhanced. Automatic terrain recognition and control mode selection maybe made with confidence.

Ride Height Control

With reference to the embodiment of FIG. 1, with the VCU 10 operating inthe manual condition a user may adjust vehicle ride height (selectingkneeling or access ride-height, on-road ride height or raised rideheight) by means of ride-height adjustment control 171 c′. Otherintermediate or discrete ride heights may also be useful and selectablein the same manner. If the user selects a control mode that requires theraised height and the vehicle has on-road ride height selected, the VCU10 prompts the user to raise the ride height by means of control 171 c′.Depending on the selected operating mode, if the user has not selected arequired PTU gear ratio, the VCU 10 may also prompt the user to select arequired ratio, for example low ratio.

If the user selects operation of the VCU 10 in the automatic condition,the VCU 10 is configured automatically to select the raised ride height.This is so that the VCU 10 may automatically change between controlmodes without being required to prompt a user to change ride height.Furthermore, the VCU 10 is configured to maintain the raised ride-heightregardless of any changes in operating mode made automatically by theVCU 10. This is at least in part so as to reduce activity of theride-height control system and associated wear on vehicle components.Furthermore, user inconvenience associated with an unexpected change inride-height may also be reduced.

In some embodiments if a ride-height adjustment is required when theautomatic condition is selected, the VCU 10 may inform a driver that aride-height adjustment will take place and request the driver to confirmthat the adjustment is permitted. In some embodiments this request forconfirmation is only issued in the event the VCU 10 has determined thatthe vehicle 100 is towing.

It is to be understood that the VCU 10 may inform the driver that theride-height adjustment will take place and request the driver to confirmthat the adjustment is permitted before adjusting the ride height. TheVCU 10 may invite confirmation that the adjustment is permitted byrequesting the driver to depress a multifunction control buttonassociated with the vehicle 100. The invitation may be displayed on thedisplay associated with HMI module 32. The multifunction control buttonmay be a control button associated with the HMI module 32. A dedicatedbutton may be provided in some embodiments by means of which a drivermay provide confirmation that the ride height adjustment is permitted.

If the driver does not confirm that the adjustment is permitted within aprescribed time-out period, the VCU 10 aborts a transition to theautomatic operating mode selection condition and remains in the manualoperating mode selection condition.

In the present embodiment, the driver may command the VCU 10 to assumethe automatic operating mode selection condition by depressing knob 172of switchpack 170, which then assumes a retracted condition. In someembodiments, if the VCU 10 subsequently aborts the transition to theautomatic operating mode selection condition without assuming theautomatic operating mode selection condition, the knob 172 is caused torevert to the deployed (raised) state indicative of the manual operatingmode selection condition. Alternatively, the knob 172 may remain in theretracted position despite the VCU 10 aborting a transition to theautomatic operating mode selection condition. A user may therefore berequired manually to release the knob 172 from the refracted position.It is to be understood that the knob 172 may be arranged mechanically tolatch in the retracted or deployed conditions with no facility forautomatic deployment or retraction of the knob.

FIG. 6 is a flow diagram illustrating a method of operation of a vehicle100 according to an embodiment of the present invention.

At step S101 the VCU 10 is operating in and causing the vehicle 100 tooperate in a manual vehicle operating mode selection condition. The knob172 of switchpack 170 is in the deployed condition, indicating the VCU10 is in the manual operating mode selection condition.

Subsequently, at step S103 the VCU 10 checks whether a user hasrequested the automatic vehicle operating mode condition by pressing onupper panel 175 of the knob 172 in order to cause the knob 172 to assumethe refracted condition. If at step S103 the VCU 10 determines that theuser has not requested the automatic vehicle operating mode selectioncondition, the method continues at step S101.

If at step S103 it is determined that the user has requested theautomatic vehicle operating mode selection condition, the methodcontinues at step S105.

At step S105 the VCU 10 checks whether suspension system 12 e is set tothe raised ride height suspension system configuration mode. If at stepS105 it is determined that the suspension system 12 e is set to theraised ride height configuration mode, the VCU 10 continues at stopS113. If the VCU 10 determines that the suspension system 12 e is notset to the raised ride height configuration mode the VCU 10 continues atstep S107.

At step S107 the VCU 10 causes a prompt to appear on the display screenof the HMI module 32 informing the user that the suspension system 12 ewill be set to the raised ride-height configuration mode if theautomatic selection condition is assumed. The prompt also requests theuser to confirm that they wish to proceed. The VCU 10 then continues atstep S109. In some embodiments this prompt is only issued if towing isdetected. In vehicles not equipped for towing, this prompt may besuppressed automatically.

At step S109 the VCU 10 determines whether the user has confirmed thatthey wish to proceed with selection of the raised ride height andassumption of the automatic vehicle operating mode selection conditionwithin a prescribed time period. If the VCU 10 determines that the userhas not provided the required confirmation within the prescribed timeperiod, the VCU 10 aborts the transition to the automatic operating modeselection condition and causes the knob 172 to assume the deployed orraised condition. If the VCU 10 determines that that the switchpack knob172 cannot be raised (for example due to a fault or obstruction) the VCU10 may remain in the instant operating mode (such as SPO or GGS) andnotify the driver to check that the switchpack 170 is not obstructed, orrefer to the user handbook. The VCU 10 then continues at step S101.

If the VCU 10 determines that the user has confirmed that they wish toproceed within the prescribed time period the VCU 10 continues at stepS111.

At step S111 the VCU 10 causes the suspension system 12 e to assume theraised ride height configuration mode. The VCU 10 then continues at stepS113.

At step S113 the VCU 10 assumes the automatic operating mode selectioncondition in which the VCU 10 selects automatically the most appropriatevehicle operating mode according to the methodology described herein,and causes the vehicle 100 to assume the selected operating mode. Insome embodiments, the VCU 10 may confirm that the ride-height is in theraised configuration mode and that the suspension system 12 e isfunctioning in an expected manner before the VCU assumes the automaticoperating mode selection condition. The VCU 10 then continues at stepS115.

At step S115 the VCU 10 suspends changes in ride height whilst the VCU10 is in the automatic vehicle operating mode selection condition. Thus,regardless of the suspension configuration mode in respect of rideheight that might be required or otherwise assumed in a given vehicleoperating mode (control mode) selected automatically by the VCU 10, theVCU 10 causes the suspension system 12 e to remain in the raised rideheight configuration mode.

It is to be understood that in the present embodiment the VCU 10 maycause ride height to reduce in dependence on vehicle speed and roadroughness regardless of the selected operating mode. In the presentembodiment, if the vehicle speed exceeds a ride height lowering speedthreshold value of 50 kph and road roughness is consistent withoperation on-highway, the VCU 10 causes the suspension system 12 e toassume the on-road ride height configuration mode. Other thresholdvalues are also useful. Once speed falls below a ride height raisingspeed threshold value of 45 kph for more than a prescribed period oftime, the VCU 10 causes the suspension system 12 e to assume the raisedride height configuration mode. Other threshold values are also useful.Other arrangements are also useful.

Embodiments of the present invention may be understood by reference tothe following numbered paragraphs:

1. A control system for a motor vehicle, the system being operable in amanual operating mode selection condition in which a user may select arequired system operating mode by means of user-operable mode selectioninput device, and an automatic mode selection condition in which thesystem selects automatically an appropriate system operating mode,wherein when operating in the manual condition and a change from themanual condition to the automatic condition is made the system selects aprescribed automatic mode selection condition vehicle ride-heightindependently of the automatically selected operating mode.

2. A control system according to paragraph 1 wherein the operating modesare control modes of at least one subsystem of a vehicle, the systemcomprising a subsystem controller for initiating control of the or eachof the vehicle subsystems in the selected one of the plurality ofsubsystem control modes, each one of the operating modes correspondingto one or mom different driving conditions for the vehicle.

3. A control system according to paragraph 2 wherein the systemcomprises an evaluator for evaluating one or more driving conditionindicators to determine the extent to which each of the subsystemcontrol modes is appropriate.

4. A control system according to paragraph 3 wherein when in theautomatic condition the system is configured automatically to controlthe subsystem controller to initiate control of the or each subsystem inthe subsystem control mode which is most appropriate.

5. A control system according to paragraph 2 wherein the operating modesare control modes of at least one vehicle subsystem selected fromamongst an engine management system, a transmission system, a steeringsystem, a brakes system and a suspension system.

6. A control system according to paragraph 5 wherein the operating modesare control modes of at least two vehicle subsystems selected fromamongst an engine management system, a transmission system, a steeringsystem, a brakes system and a suspension system.

7. A control system according to paragraph 2 wherein in each systemoperating mode the system is configured to cause each one of a pluralityof vehicle subsystems to be operated in a subsystem configuration modeappropriate to the driving condition.

8. A control system according to paragraph 7 wherein the operating modesinclude control modes of a suspension system and the plurality ofsubsystem configuration modes comprise a plurality of ride heights.

9. A system according to paragraph 8 wherein the subsystem configurationmodes of the suspension system include a first ride height and a secondride height greater than the first, the system being configured when inthe automatic mode selection condition automatically to cause asuspension system to assume the subsystem configuration modecorresponding to the second ride height.

10. A system according to paragraph 9 wherein the subsystemconfiguration modes of the suspension system include modes having N+N′different respective ride heights, where N and N′ are integer, N≧1 andN′≧1, the system being configured to choose a suspension subsystemconfiguration mode having one of the N highest ride heights when thesystem is in the automatic operating mode selection condition.

11. A control system according to paragraph 7 wherein the operatingmodes include control modes of a fluid suspension system in which fluidinterconnection can be made between suspensions for wheels on oppositesides of the vehicle, and wherein said plurality of subsystemconfiguration modes provide different levels of said interconnection.

12. A control system according to paragraph 7 wherein the operatingmodes include control modes of a steering system which can providesteering assistance, and wherein said plurality of subsystemconfiguration modes provide different levels of said steeringassistance.

13. A control system according to paragraph 7 wherein the operatingmodes include control modes of a brakes system which can provide brakingassistance, and said plurality of subsystem configuration modes providedifferent levels of said braking assistance.

14. A control system according to paragraph 7 wherein the operatingmodes include control modes of a brake control system which can providean anti-lock function to control wheel slip, and said plurality ofsubsystem configuration modes allow different levels of said wheel slip.

15. A control system according to paragraph 7 wherein the operatingmodes include control modes of a traction control system which isarranged to control wheel spin, and said plurality of subsystemconfiguration modes allow different levels of said wheel spin.

16. A control system according to paragraph 7 wherein the operatingmodes include control modes of a yaw control system which is arranged tocontrol vehicle yaw, and said plurality of subsystem configuration modesallow different levels of divergence of said vehicle yaw from anexpected yaw.

17. A control system according to paragraph 7 wherein the operatingmodes include control modes of a range change transmission and saidsubsystem configuration modes may include a high range mode and a lowrange mode of said transmission.

18. A control system according to paragraph 7 wherein the operatingmodes include control modes of a powertrain system which includes apowertrain controller and an accelerator or throttle pedal the subsystemconfiguration modes providing different levels of responsiveness of thepowertrain controller to movement of the accelerator or throttle pedal.

19. A control system according to paragraph 7 wherein the operatingmodes include control modes of a transmission system operable in aplurality of transmission ratios and including a transmission controllerarranged to monitor at least one parameter of the vehicle and to selectthe transmission ratios in response, and wherein the subsystemconfiguration modes include a plurality of transmission configurationmodes in which the transmission ratios are selected differently inresponse to said at least one parameter.

20. A system according to paragraph 1 configured to cause a change inride-height in dependence on a speed of the vehicle.

21. A system according to paragraph 20 configured when in the automaticmode selection condition to reduce ride height below the automatic modeselection condition vehicle ride-height when a speed of the vehicleexceeds a prescribed value.

22. A system according to paragraph 1 arranged wherein if the systemdetermines that the vehicle is towing a load, automatic assumption ofthe prescribed automatic mode selection condition vehicle ride-height issuspended.

23. A system according to paragraph 2 wherein one or more of the drivingconditions correspond to one or more driving surfaces.

24. A method of controlling a motor vehicle implemented by a controlsystem, the method comprising causing the system to operate in a manualoperating mode selection condition in which a user may select a repairedsystem operating mode by means of a user-operable mode selection inputdevice, or in an automatic mode selection condition in which the systemis configured to select automatically an appropriate system operatingmode,

-   -   whereby when the system is operating in the manual condition and        a change from the manual condition to the automatic condition is        made the method comprises selecting a prescribed automatic mode        selection condition vehicle ride-height independently of the        selected operating mode.

25. A method according to paragraph 23 comprising causing the vehicle toassume the prescribed automatic mode selection condition vehicleride-height independently of the selected operating mode when the systemoperates in the automatic operating mode selection condition.

26. A carrier medium carrying computer readable code for controlling avehicle to carry out the method of paragraph 24.

27. A motor vehicle control system for selecting a driving surface andfor controlling a plurality of vehicle subsystems to operate in aplurality of subsystem configuration modes in dependence on the selecteddriving surface, the system being operable in a manual operatingcondition in which a user is able to select said driving surface and anautomatic operating condition in which the system is configured toselect said driving surface automatically, wherein the system is able tobe switched between said manual and automatic operating conditions bymeans of a user-operable input device,

-   -   the system being further configured to select a prescribed        vehicle ride-height independently of the selected operating mode        when operating in the automatic selection condition.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

The invention claimed is:
 1. A control system for a motor vehicle, thesystem being operable in a manual operating mode selection condition inwhich a user may select a required system operating mode by means ofuser-operable mode selection input device, and an automatic modeselection condition in which the system selects automatically anappropriate system operating mode, wherein when operating in the manualcondition and a change from the manual condition to the automaticcondition is made the system selects and maintains a prescribedautomatic mode selection condition of vehicle ride-height independentlyof the automatically selected operating mode.
 2. A control systemaccording to claim 1 wherein the operating modes are control modes of atleast one subsystem of a vehicle, the system comprising a subsystemcontroller for initiating control of the or each of the vehiclesubsystems in the selected one of the plurality of subsystem controlmodes, each one of the operating modes corresponding to one or moredifferent driving conditions for the vehicle.
 3. A control systemaccording to claim 2 wherein the system comprises a processor programmedto evaluate one or more driving condition indicators to determine theextent to which each of the subsystem control modes is appropriate.
 4. Acontrol system according to claim 3 wherein when in the automaticcondition the system is configured automatically to control thesubsystem controller to initiate control of the or each subsystem in thesubsystem control mode which is most appropriate.
 5. A control systemaccording to claim 2 wherein the operating modes are control modes of atleast one vehicle subsystem selected from amongst an engine managementsystem, a transmission system, a steering system, a brakes system and asuspension system.
 6. A control system according to claim 5 wherein theoperating modes are control modes of at least two vehicle subsystemsselected from amongst an engine management system, a transmissionsystem, a steering system, a brakes system and a suspension system.
 7. Acontrol system according to claim 2 wherein in each system operatingmode the system is configured to cause each one of a plurality ofvehicle subsystems to be operated in a subsystem configuration modeappropriate to the driving condition.
 8. A control system according toclaim 7 wherein the operating modes include control modes of asuspension system and the plurality of subsystem configuration modescomprise a plurality of ride heights.
 9. A system according to claim 8wherein the subsystem configuration modes of the suspension systeminclude a first ride height and a second ride height greater than thefirst, the system being configured when in the automatic mode selectioncondition automatically to cause a suspension system to assume thesubsystem configuration mode corresponding to the second ride height.10. A system according to claim 9 wherein the subsystem configurationmodes of the suspension system include modes having N+N′ differentrespective ride heights, where N and N′ are integer, N≧1 and N′≧1, thesystem being configured to choose a suspension subsystem configurationmode having one of the N highest ride heights when the system is in theautomatic operating mode selection condition.
 11. A control systemaccording to claim 7 wherein the operating modes include one or more of:control modes of a fluid suspension system in which fluidinterconnection can be made between suspensions for wheels on oppositesides of the vehicle, and wherein said plurality of subsystemconfiguration modes provide different levels of said interconnection;control modes of a steering system which can provide steeringassistance, and wherein said plurality of subsystem configuration modesprovide different levels of said steering assistance; control modes of abrakes system which can provide braking assistance, and said pluralityof subsystem configuration modes provide different levels of saidbraking assistance; control modes of a brake control system which canprovide an anti-lock function to control wheel slip, and said pluralityof subsystem configuration modes allow different levels of said wheelslip; control modes of a traction control system which is arranged tocontrol wheel spin, and said plurality of subsystem configuration modesallow different levels of said wheel spin; control modes of a yawcontrol system which is arranged to control vehicle yaw, and saidplurality of subsystem configuration modes allow different levels ofdivergence of said vehicle yaw from an expected yaw; control modes of arange change transmission and said subsystem configuration modes mayinclude a high range mode and a low range mode of said transmission;control modes of a powertrain system which includes a powertraincontroller and an accelerator or throttle pedal, the subsystemconfiguration modes providing different levels of responsiveness of thepowertrain controller to movement of the accelerator or throttle pedal;and control modes of a transmission system operable in a plurality oftransmission ratios and including a transmission controller arranged tomonitor at least one parameter of the vehicle and to select thetransmission ratios in response, and wherein the subsystem configurationmodes include a plurality of transmission configuration modes in whichthe transmission ratios are selected differently in response to said atleast one parameter.
 12. A system according to claim 2 wherein one ormore of the driving conditions correspond to one or more drivingsurfaces.
 13. A method according to claim 12 comprising causing thevehicle to assume the prescribed automatic mode selection conditionvehicle ride-height independently of the selected operating mode whenthe system operates in the automatic operating mode selection condition.14. A system according to claim 1 configured to cause a change inride-height in dependence on a speed of the vehicle.
 15. A systemaccording to claim 14 configured when in the automatic mode selectioncondition to reduce ride height below the automatic mode selectioncondition vehicle ride-height when a speed of the vehicle exceeds aprescribed value.
 16. A system according to claim 1 arranged wherein ifthe system determines that the vehicle is towing a load, automaticassumption of the prescribed automatic mode selection condition vehicleride-height is suspended.
 17. A vehicle comprising a system according toclaim
 1. 18. A method of controlling a motor vehicle implemented by acontrol system, the method comprising causing the system to operate in amanual operating mode selection condition in which a user may select arequired system operating mode by means of user-operable mode selectioninput device, or in an automatic mode selection condition in which thesystem is configured to select automatically an appropriate systemoperating mode, whereby when the system is operating in the manualcondition and a change from the manual condition to the automaticcondition is made the method comprises selecting and maintaining aprescribed automatic mode selection condition of vehicle ride-heightindependently of the selected operating mode.
 19. A non-transitorycarrier medium carrying computer readable code for controlling a vehicleto carry out the method of claim 18.